Lightweight composite building construction

ABSTRACT

Lightweight composite structures, mostly of profiled sheet metal, comprising a main joist formed from two outer sheaths interconnected by rigidifying bridges. Each sheath comprises a web with end flanges, the end flanges of one sheath being directed towards the flanges of the other sheath. Each mutually opposed pair of flanges are spaced apart to provide a slot providing access to a housing within the joist and defined by the bridge and the sheaths. The bridges also provide the means whereby the main joist and other similar joists and accessories may be interconnected to produce frameworks, divisions, walls, partitions, ceilings, shelving, articles of furniture and the like, for industrial and private use.

@nited States Patent Vincens Sept. 11, 1973 [75] Inventor: Rene Vincens, Ancourt Par Neuville Les Dieppe, France [73] Assignee: Societe dEtude et de Promotion dEntreprises [22] Filed: Oct. 4, 1971 [21] Appl. No.: 186,188

[52] US. Cl 52/731, 52/632, 52/36, 52/238 [51] Int. Cl. A47f 5/00 [58] Field of Search 52/730, 731, 732, 52/238, 588, 580, 36, 632

[56] References Cited UNITED STATES PATENTS 1,360,720 11/1920 Brown 52/731 2,082,792 6/1937 Dean..... 52/731 2,356,309 8/1944 Garbe 52/731 2,589,304 3/1952 Spangler... 52/731 2,930,665 3/1960 Bandai 52/730 FOREIGN PATENTS OR APPLICATIONS 125,748 4/1919 Great Britain 52/730 329,284 4/1958 Switzerland 52/730 Primary Examiner-Frank L. Abbott Assistant ExaminerHenry E. Raduazo Attorney-Robert E. Burns et al.

[57] ABSTRACT Lightweight composite structures, mostly of profiled sheet metal, comprising a main joist formed from two outer sheaths interconnected by rigidifying bridges. Each sheath comprises a web with end flanges, the end flanges of one sheath being directed towards the flanges of the other sheath. Each mutually opposed pair of flanges are spaced apart to provide a'slot providing access to a housing within the joist and defined by the bridge and the sheaths. The bridges also provide the means whereby the main joist and other similar joists and accessories may be interconnected to produce frameworks, divisions, walls, partitions, ceilings, shelving, articles of furniture and the like, for industrial and private use.

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sum 11 ur 15 PATENTEU SEP] 1 I973 sum 12 or PATENTED I 1 75 SHEU 13 0F 15 PATENTEDSHHIB'IS v 3-757 4 I sum 150F15 LIGHTWEIGHT COMPOSITE BUILDING CONSTRUCTION The present invention relates to light-weight composite structures formed by the combination of standardized elements, structures which concern the building industry, its fittings and equipment, made of rigid and semi-rigid materials, to supply composite structures enabling homogeneous panels to be produced in the most widely varying shapes, these panels being themselves combinable for the purpose of creating homogeneous assemblies. The light-weight composite structures produced from the standardized elements according to the invention may equally well consist of light frames, devisions, partitions, ceilings, false ceilings, walls, fixed or movable joinery units for building proper, industrial fittings, commercial or private furnishings in general.

ln the sphere of construction, buildings, of light weight and preferably prefabricated, as well as all their fittings, require materials having the following characteristics: the structures must be rigid, elegant in appearance, as light in weight as possible, economical and with as few points as possible where the various types of corrosion can occur, an object which must be achieved, in particular, by the elimination of welds between external sections. Furthermore, these structures must be capable of being assembled rapidly, to form panels, at the assembly workshop stage, and the panels and their accessories must be such that they can as far as possible be erected immediately on the users premises, by means of rigid connections, without recourse to screws or bolts, thus facilitating the storage, packing and transport problems.

For this purpose, one of the first aims of the invention is to use composite structures formed from elements of which the manufacture is as simple and as standardized as possible, these elements being of a modular nature and preferably making use of the thin-metal profiling technique, making evident the quality of the surface treatment undergone by the metals employed and the dimensional stability of these sections, which do not have to be, welded together. Finally, thanks to the extremely small number of accessories, the elements can be stored and transported, causing only a minimum volumetric loss and entailing no risk of corrosion whatever. All the profiled elements and accessories can be manufactured continuously and in large quantities, either on a regions] or on a national basis, and thus at very low cost. 3

The elementary profiles whichmake up the bearing, fastening and binding supporting structure, likewise serve to make up bearing, fastening and binding panels, of variable sizes and shapes, of which the external and visible surfaces are functionally and aesthetically coordinated, at the same time enabling assemblies of a homogeneous and harmonious style and design to be produced. The panels are also so designed that they can accommodate removable and/or mobile fittings, such as doors, drawers or brackets, these fittings being themselves produced from elements forming the bearing, fastenings and binding supporting structure, which can likewise accommodate or comprise functional and decorative materials in the form of slabs of modular dimensions, thus rendering the assemblies still more attractive and economical.

Thanks to the elimination of the welds on the external sections, any desired materials can be used, such as prelacquered steel, stainless steel, aluminium or plastics. This use of new materials enables an infinite variety of ornamental combinations to be obtained by the different ways in which the materials and colours can be combined, and by the solely functional combinations obtained by the inclusion of plastics, wood and fabrics, for example, inter alia for sound-proofing and heat-insulating purposes.

A further advantage offered by the standardized constructional elements forming the light-weight structures to which the invention relates resides in the fact that, regarded as essential elements of a structure, they can be reutilized as essential elements of all the composite structural combinations required for the purpose in view, and also closely combined, in order to utilize them in the optimum manner in each of these cases.

The multi-purpose use of the composite structures to which this invention relates, as well as their applications in fittings and furnishings of buildings, show the proportional and modular character of the dimensions, since the said structures, among other advantages, enable the assemblies to be constructed to be given a certain minimum weight, combined with the use of very light sections, even if the material consists of steel, and also make it possible to obtain a certain minimum rigidity, partly thanks to the profiling, which also enables use to be made of the functional character of the folds in the metal, and the said limits to be modified by gradually increasing the strength and rigidity of the structures without thereby altering their external appearance,'the assemblies consequently being standardized, whatever the dimensions of the homogeneous assemblies obtained, and particularly in accordance with the fittings or furnishings adopted as a typical example for the application of the present invention.

Thus, on the basis of the same modular profiled sections, the production of a very light assembly of 0.8m in height, for example, can be considered just as easily as that of a high assembly, eg of 4 metres, without the I need for any alteration to the appearance of these modular profiled sections, the difference merely occurring at the level of the core of the composite structure, this latter being reinforced to a greater or smaller extent according to the circumstances of the adaptation required.

A further essential object of these structures, which, owing to the conception on which they are based, have been termed light composite structures throughout the present description, is both economical andsocial. The fact is that they enable small or medium local concerns, only having moderate overheads, and even having a limited amount of equipment, space or skilled labour, to construct and produce, close to the users premises, definite assemblies in the form of light buildings, their fittings and furnishings, with a small number of rudimentary standardized constructional elements, defined according to the presentinvention; they also enable the said concerns to be more or less competitive in relation to the current standardized products of large concerns and also to offer their clientele the possibility of producing assemblies of exceptional dimensions from the same standardized elements, of very high quality, at a cost almost as low as that of mass products of more limited presentation and dimensions.

To sum up, the multi-purpose utilization of the basic units is rendered possible by the invention, which consists:

a. of bearing composite structures proper;

b. of intermediate and low connections, of the fastening and binding, also of the squaring type, between the said original composite structures, the said connections likewise based on rudimentary standardized constructional elements forming the bearing supporting structures;

c. vertical, horizontal, lateral, fixed or mobile walls,

adaptable to the aforementioned composite structures, and consisting, in their main parts, of standardized elements constituting the said composite structures of (a) and (b).

To these constituent elements, needless to say, it is possible to add complementary fillings of different dimensions but of a strictly similar design, in order to maintain the homogeneity and the design of the entire system. Any complementary and standard filling, however, could be adopted on the basis of other materials not mentioned.

The production of standardized elements by profiling, in order to obtain a rigid structure of use in the manufacture of furniture or in the construction buildings, is obviously very well known, and existing prior art in this sphere is extensive.

For example, use is currently made of metallic elements, but these latter suffer from the drawback of consisting of comparatively thick sheet metal, to ensure the desired strength, in the various applications. These elements and consequently the structures produced from there are of considerable weight. in the present case, thanks to the original method of assembly according to the invention, and also to the special cross section presented by the various composite joists, the principal and the secondary one, use is made of thin metal elements, since the sheet metal of which they consist generally measures four to five tenths of a millimetre; the special way in which the various standardized elements fit into one another, according to the present invention, enables excellent physical characteristics to be obtained, particularly as regards strength.

Now that plastic materials are available, all possible profiled shaped can be considered, owing to the main characteristic of the said materials, i.e., the fact that they can be extruded. In actual fact, however, plastics are only of advantage for small items in which problems of shaping play an important part, but their use cannot be seriously considered in simple profiling operations for which metal, of equivalent strength, costs less; the fact is that, assuming equal strength, plastics of two or three mm in thickness are required to replace steel plates of only three to four tenths of an mm in thickness, a circumstances which is by no means in favour of plastic.

In conclusion, assemblies according to the invention can in theory be produced on the basis of profiled sections obtained by the extrusion of a plastic material, but these sections would not have the required physical characteristics or else would prove far too expensive; within the framework of the present invention, therefore, use is made of metallic profiled sections of a thickness substantially equal to four or five tenths, for a large number of applications, and the said sections, if it proves necessary, can be assembled more firmly by means of adhesives, the setting and even the welding process (as in the case of galvanized steel). In some cases, for reasons of economy or simplification, one or more parts of the said profiled section can be obtained on the basis of a plastic material, provided the demands made on the said parts where their physical properties are concerned are very moderate.

Among the best known previous techniques and similar partial applications, some of the said techniques necessitate cuts in slabs of material or profiled sections, the said plates and profiles being assembled by welding when they are of metal. A feature common to these techniques is that after the preparation of the elements or assembled articles of furniture they are given a surface finish, which in the nature of things necessitates considerable investments and the setting up of large factories. The fact remains, however, that the sheathings obtained with these latter techniques are mediocre from the point of view of quality, or else very expensive, and sometimes very difficult to produce.

Closed tubular profiles are also known, interconnected by means of standard angular parts, which may or may not be visible; this technique precludes the treatment of the surfaces by the continuous belt system and does not enable binding and squaring panels to be produced, an important characteristic of the composite structures produced by the present invention. (French Pat. Nos. 1,561,389 and 1,561,562 illustrate this previous technique).

A common application, which is, in fact, extremely usual in Europe, consists of the use, for furniture, of a framework in the form of drawn joists of a luminium, which are either quadrangular or octagonal, forming on each surface as or dovetails, to which, by means of screws or bolts, initial devices can be affixed for angle(L) connections. These units may or may not fit the hollow retaining part in the joists. A common feature of all these latter is a not easily modifiable appearance and the fact that they are not designed to form homoge neous panels from which it is possible to produce, when desired, not only joists but also walls and shelves etc., which can be interconnected without either screws or bolts. Furthermore, for a certain particular modular type, these joists are either too heavy or too light, according to their purpose.

Among the large number of types of shelf at present in existence, some consist of more or less perforated uprights, which necessitate, owing to the weakening caused by these holes, the use of steel of about 2-5 mm in thickness, while others consist of solid uprights of a certain width, necessitating the use of steel of eight to 15 tenths of an mm in thickness. In both cases, whether the units are solid or hollowed out, the uprights are not designed to form panels which can be combined with one another longitudinally and thus varied in width. These shelf uprights are generally rectangular, while the invention enables homogeneous, combinable panels to be constructed of which the base can be of a different width from that of the central zone, which itself differs in width from the top. Furthermore, the shelf systems are characterized by connections which prevent them from being suitable, for example, for a living room, whereas the invention, thanks to the aesthetically satisfactory invisible nature of its rigid and economical connections, can fit conveniently into a living room without being thereby rendered unsuitable for industrial use. Finally, the invention gives preference to the use of profiled external plates of a thickness of 4-5/10 mm, the economy of which could not easily be surpassed. This invention, of which certain elements can form a shelf system, is thus more similar to a kind of metal cabinet-making system for industrial purposes, thanks to the possibility of including standard profiled sections, of varied colours and with ornamental sheathing, thus differing completely from the known industrial shelf systems.

Existing prior art can be advantageously completed by a study of the following main patents:

Brit. Pat. No. 125,748 describes a joist consisting of two parallel longitudinal castellated channel-sections, symmetrical and back to back, necessarily interconnected by welding, riveting or bolting along the central web of these profiles. These joints, however constructed (e.g. two U-sections with a concave web with turned flanges, or two C-sections placed back to back with a tubular bridging), are not provided, on a level with the flanges of the section, with any retaining means, so that between the extremities of these profiled sections, face to face, it is impossible for devices constituting an initial basis for orthogonal connections to be rigidly locked in position. Furthermore, the joists thus formed are unaesthetic, as the sections and bridges(- stuts) are completely visible; their use thus cannot be considered for a high-quality article of furniture, in which every joist and every panel consisting of elements similar to the joist must have an impeccable finish. In conclusion, particularly owing to the impossibility of considering orthogonal lateral connections based on the struts of the joist, the latter must be regarded as a unit having an unfortunate passivity, so that it can underno circumstances consitutute a composite structure for the construction of fittings and furniture in the building industry.

Brit. Pat. No. 381,771 describes an assembly of S-channels arranged face to face, for the production of a joist which similarly lacks the aesthetic and technological advantages of the present invention. The C- sheaths are assembled by means of a totally internal connection piece taking the form of a very thin lightweight strut, which thus cannot serve as an efficient base for squaring-connections. The resulting joist consists of continuous profiles describing an enclosed space, inaccessible from outside and not allowing of any other cooperation than that obtained by means of screws, bolts, gudgeons etc. Finally, the continuous sheaths, mainly of metalqare necessarily of considerable thickness, in order to give the joist as a whole a sufficient rigidity over its entire length, the said joist having no internal stiffener, since the struts are too thin to fulfil this purpose.

Brit. Pat. No. 636,517 describes a joist produced by assembling two C-sections face to face, similarly to the method of assembly mentioned in the preceding paragraph. In this case the continuous external sheaths are interconnected by a likewise continuous central core which delimits, between the extremities of the sheaths, two symmetrical longitudinal housings, but since no longitudinal cavity freely accessible from outside the joist is set back from each space, it is impossible to provide perpendicular or parallel connections between two joists. Each joist claimed in the present patent is solely designed to accommodate a furnishing wall (furniture panel) in each of its longitudinal spaces; no lateral extension at the same level as the joist is feasible; finally, it suffers from the drawback that the assembly of a joist and of a wall introduced into a space therein can only be effected with screws and bolts, since this joist, like the others mentioned, has no retaining device and is absolutely passive.

French Pat. No. 1,285,261 describes ajoist produced by assembling cast aluminium profiled sections provided with longitudinal racks. Here again, owing to the inaccessibility of the core of the joist, it is impossible to define squaring-connections at any level, and the unions between the joists become impossible except at the top and bottom ends. Furthermore, the locking systems of the unions are complex, as they are based on the use of screws, nuts and gudgeons. All along the joist, both the external sheaths and the core are uninterrupted, so that each joist is heavy. Finally, unlike the assembly produced by the present invention, the core only functions as an internal stiffening device for the sheaths and plays no part in the orthogonal lateral connections.

Finally, French Pat. No. 1,381,274 describes a quadrangular column obtained by the interconnection of two castellated profiled sections at the level of their webs, and to this extent it resembles the joist covered by Brit. Pat. No. 1,257,481. The fact is that the profiled sections are welded together by their webs and do not comprise any retaining flanges enabling any other joist, whether parallel or orthogonal, to be fixed. Articles of furniture produced from such joists do not fulfil the aesthetic requirements of the present invention, since the castellated profiles, and the dovetails included therein, are totally visible, and this could not form an article of furniture of impeccable finish. The joist in U.S. Pat. No. 1,381,274, furthermore, does not have the property of modifying its resistance in accordance with a certain standard, since, being continuous, it is of the same thickness from one end to the other; neither does it enable the density to be varied along the joist. In the comers of the structure, free accessibility to the spaces provided between two profiled sections is rendered impossible by the presence of lateral connection devices; free accessibility, when provided in other parts of the joist, is at all events limited to the use of the dovetail and of the longitudinal space of the castellated profile, mainly to enable wooden panels to be introduced. The connections in themselves are fairly complex, since most of them are provided by means of screws, gudgeons and even jacks. To conclude, the sole purpose of a joist of this kind is to construct a homogeneous panel in which the profiled sections used for the said joist are at the same time the elements of which the panels consist. Taken as a whole, the purpose served by the said patent is only part of that served by the present invention, which is of a general nature and applicable to all buildings and their fittings.

Among the numerous advantages of the construction to which the present invention relates, particular mention may be made of the following:

constant free access to the longitudinal housings, even in the corners of the structure, whether in a panel or a joist or from one panel to another or from one joist to another;

external sheaths covering each joist, creating an aesthetic uniformity and at the same time establishing the minimum rigidity for materials of small dimensions;

the assembly of the sheaths to the central core is provided without screws, bolts or welding, so that the sheathson the one hand and the stiffening cores on the other are rendered totally independent. Consequently, and whatever the material used, since there is no longer any limit, the only study required for the material relates to sufficient rigidity and mechanical strength, and this in no way prevents each joist and each panel from constituting an assembly nevertheless remaining entirely homogeneous.

the presence of sheaths renders the central core, provided in the form of a bridging, and the orthogonal connecting elements, absolutely invisible,

the stiffening core may, if required, form a swuaring-base towards all sides, in the plane perpendicular to the axis of the joist;

all the visible surfaces are aesthetically acceptable: the system defines two plane surfaces prolonged by the continuous webs of thw two external sheaths, and two continuous and even longitudinal spaces between the extremities of the said sheaths;

the core of the joist is non-continuous, and this reduces the weight of the latter in addition to enabling the density to be varied in the longitudinal direction, which is in accordance with the main technological purpose of the invention. The special cut presented by the central core renders the joist very rigid but at the same time very light in weight, and extremely thin and light material can be used for the said joist. According to circumstances and the central core used, the strength and rigidity of each joist can be varied, zone by zone, in accordance with the needs arising;

the light composite joists thus constructed enable a great variety of articles of furniture to be assembled, and conversely, the said articles can be dismantled without loss of time, either to reconstruct an exact model of the article of furniture required or to convey the material to premises where the initial article of furniture can be re-assembled without difficulty. Transformations of articles of furniture, particularly extensions thereto, are effected in accordance with the users exact requirements, owing to the easy method of assembly;

owing to the standardization and ease of assembly, any town or city can have, on the spot, an assembly workshop equivalent to a factory.

According to the main characteristic of the invention, a light-weight composite structure, formed by the combination of standardized metallic elements and possibly including at least one part made of a plastic material, the said elements being themselves homogeneous and combinable, the said structure being intended for building construction and for the relevant fittings and furnishings, is characterized by the fact that it comprises at least one main composite joist consisting of two external parallel sheaths, each comprising a central web and two flanges constituting projecting retaining devices and arranged face to face in such a manner that their projections are directed towards one another, while independent elements, acting as stiffeners for the sheaths and constructed as initial bridges of variable length, spaced out from one another in the Iongitudinal direction, function as symmetrical struts for the said sheaths, in such a way that they delimit, between each pair of mutually opposite projections, a functionally and aesthetically satisfactory longitudinal space, of regular width, the first two bridges delimiting two longitudinal housings between the external sheaths, each positioned to the rear of each space, in such a way that each housing is freely accessible from outside the said joist, each bridge being also capable of constituting a squaring-connection, in a plane perpendicular to the axis of the main joist, with a second joist.

According to a second characteristic, the lightweight composite structure comprises, in combination with at least one main joist, a secondary composite joist, parallel and complementary to the main joist, consisting of two parallel external profiled sections arranged face to face and each having a central web, substantially flat, contacting the plane of the external sheath of the main joist and two marginal retaining flanges, the gap between the pairs of flanges opposite the said profiles being at least equal to the said space, while second bridges of variable length, spaced out from one another in the longitudinal direction symmetrically strut the sad profiles, the said second bridges each comprising a central web provided, beyond each web of the profiles, two flexible symmetrical longitudinal returns, gripping the extremities of the marginal retaining flanges of the two external profiles, introduced longitudinally into one of the two housings of the main joist, the flanges of the external profiles being gripped between two projecting retaining devices opposite the external sheaths of the main joist, each second bridge being also capable of forming a squaring-connection.

A description will be given hereunder, by way of an example, without any limitative effect, of various ways in which the present invention can be designed and constructed, by reference to the accompanying drawings, wherein:

FIGS. la and lb are views in perspective, showing ex' amples of models of furniture constructed with composite structures in accordance with the invention.

FIG. 2 is a view in cross section of the preferred main joist for the invention.

FIG. 3 is a cross section through a variant of the main joist shown in FIG. 2, in which said variant the flanges forming the projecting retaining devices are constructed in the form of flanges possessing longitudinal ribs.

FIG. 4 is a cross section through a version of the main joist in which each projecting retaining device takes the form of one single squaring flange which is thin by comparison with the web of the external sheath.

FIG. 5 is a view, in perspective, of a main joist in which the internal strut consists of two lateral clamps of a C profile, interconnected by means of a tubular quqdrangular enclosure.

FIG. 6 is a cross section through a variant of the main joist shown in FIG. 5.

FIGS. 7 and 8 are a view in perspective and in profile, respectively, of a main joist, in which the internal strut consists of4 U-channels themselves defining the tubular central enclosure.

FIG. 9 is a view, in perspective, of a variant of the main joist of FIG, 7.

FIGS. 10a and [0b are views, in perspective, of an external sheath of the main joist along which the two possible contructional versions of the bridging struts are arranged modularly.

FIG. 1! is a view of the extremity cross section of an assembly of main and secondary joists, in which assembly the main joist, situated at the top, is the preferred constructional version of the present invention.

FIG. 12 is a cross section ofa main joist of which the internal strut is solid.

FIG. 13 is a cross section of a variant of the joist of FIG. 12, in which variant the strut, constructed as ajuxtaposition of U-channels, is substantially solid. 

1. A lightweight composite structure, comprising at least one main composite joist consisting of two external parallel disposed sheaths, each sheath comprising a central web and two flanges constituting projecting retaining devices, and arranged face to face in such a manner that their retaining devices are directed towards one another, a plurality of first stiffening bridge means comprising means disposed internally of the sheaths interconnecting the sheaths and functioning as symmetrical struts for the sheaths and spacing them so the sheaths define between each pair of mutually opposite retaining devices a longitudinal slot of constant width, the plurality of first bridge means being spaced from one another in the longitudinal direction of the joist and frictionally engaging the sheaths for selective positioning thereof in spaced positions in said longitudinal direction, said bridge means defining two longitudinal housings between the external sheaths, one housing being positioned to the rear of each slot, in such a way that each housing is freely accessible through the slot from outside the said main joist, each first bridge means constituting means for providing a squaring-connection between two main joists.
 2. A structure in accordance with claim 1, comprising in combination with at least one main joist, a secondary composite joist, parallel and complementary to the main joist, the secondary joist consisting of two parallel disposed external profiled sections, arranged face to face and each having a substantially flat central web substantially co-planar with the plane of the web of an external sheath of the main joist and two marginal retaining flanges defining a gap there between opposite said profiled sections being at least equal to the width of the slot, a plurality of second bridge means, spaced from one another in the longitudinal direction of the secondary joist and functioning as symmetrical struts for the said profiled sections, said second bridge means each comprising a central web having two flexible symmetrical longitudinal returns which grip extremities of the marginal retaining flanges of the two external profiled sections, the webs of the second bridge means extending longitudinally into one of the two housings of the main joist, the flanges of the external profiled sections being gripped between two mutually opposed retaining devices of the main joist, and each second bridge means also constituting means for forming a squaring connection between the joists.
 3. A structure according to claim 2, wherein at least one of the first bridge means of the main joist consists of two lateral grippers constructed in the form of longitudinal C-shaped cross section profiled units each comprising an uninterrupted or perforated web with a flange at each end, the said grippers, on the one hand, being aranged in such a manner that the flanges on one web extend in a direction opposite to the flanges on the other web, while on the other hand the webs are joined by a quadrangular, solid or tubular enclosure, the said one first bridge means thus defining, inside of its two lateral grippers, a C-shaped cross section longitudinal housing.
 4. A structure in accordance with claim 3, wherein said web comprises intrados and in which at least one of the first bridge means of a main joist comprises two symmetrical longitudinal castellated cross-section profiled units, each comprising a central web parallel to the webs of the external sheaths and two marginal flanges bearing against the intrados of the web of one of the two external sheaths, the said marginal flanges being each prolonged by a return bearing against one projecting retaining device of the external sheath, the width of the central web of each castellated profiled unit being at least equal to the gap between the two marginal flanges of said castellated profiled unit, the said two castellated profiled units also being joined to each other in such a manner that at least parts of their respective webs are situated opposite to each other and that they define longitudinal C-shaped cross-section housings.
 5. A structure in accordance with claim 4, wherein the two castellated profiled units connecting the two external sheaths of a main joist are joined by a connection piece of which the central web bears against at least part of the web of each castellated profiled unit and is prolonged by at least four longitudinal returns, enabling two castellated profiled units to be joined to each other, the external surface of the web of each castellated profiled unit associated with an external sheath being situated in the plane passing through that point of the projecting retaining device of the said external sheath which is nearest to the longitudinal plane of symmetry of the main joist, in such a manner that the thickness of the said connection piece is equal to the width of the said slot.
 6. A structure in accordance with claim 5, wherein the external surface of the web of each castellated profilled unit has at least one protuberance facing a corresponding protuberance on the other web, the sum of the heights of the two opposed protuberances being equal to the width of the said slot.
 7. A structure in accordance with claim 6, wherein at least one of its corners comprises two orthogonal disposed main joists connected together by a ''''square'''' or angle piece, each of the two branches of the latter being locked between and in contact with the webs of the two castellated profiled units respectively of the first and of the second main joist, while that part of the second orthogonal branch of the said ''''square'''' or angle piece which passes through the said slot provided between the projecting retaining devices of the external sheaths of the second orthogonal main joist is of a thickness equal to the said slot, in such a manner as to provide between the said main joists a connection of the ''''squaring or lateral'''' type as hereinbefore defined.
 8. A structure according to claim 7, wherein one of the two branches of the ''''square'''' or angle piece has perforations congruent with the protuberances on the castellated profiled units connecting the external sheaths of the main joists.
 9. A structure in accordance with claim 8, wherein at least one of the transversal or longitudinal sides of the ''''square'''' or angle piece comprises means, which are constructed, for example, in the form of hooked teeth for securing the said ''''square'''' or angle piece in each of the main joists which it connects orthogonally, the said teeth interacting with and passing through perforations in the central web of the castellated profiled units and in the web of the connecting pieces, and locking means, which are constructed, for example, in the form of clips positioned opposite the internal surface of the central web of the castellated profiled units, thus locking the said teeth and preventing them from working loose and leaving the castellated profiled unit within which they are enclosed.
 10. A structure in accordance with claim 9, wherein at least one of its corners comprises two orthogonal main joists connected together by the ''''perpendicular'''' system hereinbefore defined, i.e., a first main joist in which the bridge means used for the ''''squaring'''' connection is formed by two castellated profiled units fixed back to back, and a second main joist, from the end of which at least one tooth extends, prolonging the branch of an Angle piece locked between the webs of the two castellated profiled units of the said second main joist, while that castellated profiled unit of the first main joist which is remote from the second main joist extends beyond the end of the said first main joist by a length equal to the distance separating the webs of the two external sheaths of the second main joist, in such a manner that the web of the said castellated profiled unit extending beyond it is traversed by the said tooth, and means for locking the said tooth being provided opposite the internal face of the central web of the extending castellated profiled unit.
 11. A structure in accordance with claim 10, wherein at least one of its corners comprises two orthogonal main joists, interconnected by the ''''squaring'''' system as hereinbefore defined, the central gap between the webs of the two castellated profiled units of the first main joist being accurately calibrated in such a manner that the second branch of the angle piece locked in the second main joist is slid into position between the said castellated profiled units of the first main joist in such a way that at the same time the intermediate flanges of the external sheaths of the second main joist are in close contact with the end cross section of the two castellated profiled units of the said first joist, in order to prevent the angle piece from bending at its most fragile part.
 12. A structure in accordance with claim 11, wherein at least one joist comprises an L-shaped, T-shaped or X-shaped gripper, of which each branch consists of two arms of U-shaped cross section profile, which are face to face and symmetrical, each of the said arms having a configuration identical with that of the longitudinal cavity defined between the central part of the castellated profiled unit and the intrados of the central part of the web of the external sheath associated with the said castellated profiled unit, each arm of each branch of the said gripper being introduced into one of the said cavities, in such a way as to provide, between at least two main joists, an orthogonal connection of the ''''perpendicular'''' type or else a unidirectional prolongation.
 13. A structure in accordance with claim 12, wherein the central web of at least one of the second bridge means of a secondary joist, associated with and complementary to a first main joist, is provided over at least a part of its length with locking means capable of passing through the longitudinal space provided between two mutually opposite projecting retaining devices of a further second main joist orthogonal to the main and secondary joists already mentioned, while the external sheaths of the further second main joist are situated in the plane of the sheaths and of the external profiled units respectively of the said first main joist and of the secondary joist, while at least one of the two external sheaths or at least one of the first bridge means of the second main joist also comprises devices for locking the said means.
 14. A structure in accordance with claim 13, wherein at least one main joist is provided, on at least one of the ends of at least one of the two external sheaths of the said joist, with a finishing cap, for functional and aesthetic purposes, and made of metal or plastic, and covering the four non-sheathed surfaces of the extremity of the said main joist, the said cap consisting of a profiled part with a straight section identical to that of an external sheath of the said main joist and comprising, in particular, longitudinal retaining flanges and similar to the projections of the said main joist, in such a way that the removal of the said cap allows access to locking means in the said main joist, to enable accessories or a second main joist to be attached thereto. 